1. Field of the Invention
This invention relates to queuing for each virtual channel (VC) in an asynchronous transfer mode (ATM) exchange, and more particularly to an arbitration method for output cells of an ATM and an arbiter circuit.
2. Description of the Related Art
Conventionally, an ATM exchange adopts a method of storing cells of each virtual channel into an individual queue (per-VC queuing) in order to achieve fine traffic control.
The per-VC queuing method is used also for VC merging and so forth when MPLS (Multi-Protocol Label Switching) is incorporated in an ATM exchange.
Such queuing for each virtual channel of an ATM exchange as described above is disclosed, for example, in Japanese Patent Laid-Open Nos. 224364/1998 and 191774/1999 and Japanese Patent No. 2797989. Japanese Patent No. 2797989 discloses a cell traffic shaper which queues cells into a cell buffer for each logically multiplexed connection or connection group and controls the output cell rate from each queue using a plurality of timers. When a first cell is stored into a queue, a corresponding timer is assigned to the queue and set, and if the queue becomes empty, then the setting of the timer is cancelled so that the timer is released from the queue.
However, while use of the “per-VC queuing” method makes traffic control for each VC possible, there is the possibility that a very great number of queues such as several tens thousands queues may be involved.
This gives rise to a problem that a long processing time for arbitration is required for the output and processing may not be completed within a fixed period of time.